Speckle-free laser illumination in the visible, infrared (IR) (e.g., IR (NIR), short-wave IR (SWIR), mid-wave IR (MWIR), or long-wave IR (LWIR)) and ultraviolet (UV) bands of wavelengths are of interest for several commercial, industrial, scientific and military applications. Laser illumination, for representative purposes of imaging and targeting objects, and distinguishing friend from foe, is of major interest to the military, especially at eye-safe wavelengths. SWIR illuminators are of particular interest because light at the SWIR wavelength is reflected by objects just as visible light is and enables imagery for identification through shadows and contrast.
Speckle can be eliminated by employing incoherent sources such as LED's. Lasers, on the other hand, provide the advantages of high power, low divergence and high brightness. The inherent coherence, both temporal and spatial, of lasers however results in speckle formation. Speckle in laser illumination is undesirable in imaging and targeting applications. One laser source for such low-speckle illumination is a vertical cavity surface-emitting laser (VCSEL) array. However, high power VCSEL arrays are not yet available at SWIR wavelengths. Thus, it would be desirable to reduce speckle utilizing conventional coherent lasers that are applicable to SWIR wavelengths and can also be used at other wavelengths, such as UV, visible or other IR bands.